Increasing use of wood and wood like structures in the field of architectural constructions creates a demand for specialized hole saws to cut holes for plumbing, piping and the like at the construction site. Special hole saws such as the cross referenced I-joist Hole Cutting Apparatus are invented to provide for on site fabrication of ever increasing hole diameters with common handheld power drills. The wheel like body of the I-joist Hole Cutting Apparatus has a solid rim that provides a relatively large momentum of inertia reducing the risk of sudden tool locking, which eventually causes the power drill to be ripped out of the operator's hands. The large momentum of inertia in turn causes relatively large gyroscopic forces opposing a tilting or wobbling of the rotating power tool.
To reduce the operational torque necessary to cut large diameter holes, the I-joist Hole Cut Apparatus may be moved in a slight wobble movement around the pilot drill's centering hole. The peripherally rotating cutting blades thereby engage only partially in the cutting groove. This results on one hand in reduced friction between cutting blades and the side walls of the cutting groove and on the other hand in increased cutting pressure at the bottom of the cutting groove. Cutting pressure is ideally brought to a feasible maximum to increase the rate of chip removal. Unfortunately this causes, in combination with the wobble movement and the gyroscopic forces, a significant tilt torque that needs to be communicated between the power drill and the power tool.
Hole saw bodies commonly provide a radial structural connection between the peripheral cutting elements and the central arbor, which in turn is chucked in a power drill. The central arbor needs to be made from high strength material such as steel or steel alloy to match the mechanical properties of the power drill's chuck, to keep wear to a minimum and to withstand operational load torque and eventual tilt torque. The hole saw body has features that correspond with the arbor features to define an arbor system in which various diameter hole saw bodies are alternately connected with the arbor, without removing the arbor from the chuck. As hole saw diameters increase, material and fabrication costs of the hole saw body force the industry to select inexpensive low strength materials and fabrication techniques. This in turn increases discrepancies of mechanical properties of arbor and hole saw body.
Prior art arbor systems commonly provide a connection between hole saw body and arbor via a central thread hole screwed onto a thread bolt of the arbor. The hole saw is operated in accordance with the thread orientation such that the torque transmitted via the chuck and the arbor causes the thread to tighten. To remove the power tool from the arbor, tool and arbor need to be rotated with respect to each other in direction opposite the operating torque. This requires usually additional hand tools to engage with the arbor and the power tool. Debris in the thread interlock, excessive operational torque eventually resulting from sudden tool locking and/or eventual corrosion in the thread interlock may cause thread locking. Thread locking may render a removal of the power tool from the arbor difficult if not impossible with conventional means.
The problem of thread locking has been addressed in the prior art by transmitting the operational torque via additional interlocking features such as driving pins that extend from the arbor commonly in an axial direction at an offset from the central thread bolt. The power tool features pin holes at an offset corresponding to that of the driving pins such that after screwing on of the power tool to the arbor, the driving pins may be aligned with corresponding pin holes at certain orientations of the power tool relative to the arbor. In the prior art arbor systems, the driving pins are commonly held axially moveable and circumferentially rigid with respect to the arbor's thread bolt and may be engaged with the pin holes once aligned with each other. Because the driving pins transmit the operational load torque from the arbor via the pin holes onto the power tool, the central thread connection remains relatively lose irrespective of the operational torque. Disassembly of the power tool is therefore easily accomplished by axially removing the driving pins from the driving holes, followed by unscrewing the central thread connection.
A significant shortcoming of prior art arbors, having axially moveable driving pins and a central thread connection, is that due to the defined circumferential orientation between the arbor and the power tool and necessary tolerances between arbor and power tool, the assembled power tool remains loosely attached to the arbor's thread bolt. This prevents precise control of the power tool. More importantly, the above described tilting torque that may need to be transmitted onto the power tool via the thread connection is very limited due to the loose interlocking of both threads.
Construction workers operate tools in a rough and fast paced manner. Exchanging hole saws may likely be performed without verification of a proper tightening of the tightening features and eventually even without use of tightening tools. A reliable arbor system may need a snap feature to prevent inadvertent loosening between the arbor and the hole saw during operation. Prior art quick release arbor systems utilize a number of relatively intricate elements to provide snap in and/or ratchet features that may be sensitive to debris, rough handling and that may be difficult to maintain and replace.
For the reasons presented above, there exists a need for an arbor system that on one hand provides easy assembly and disassembly unaffected by the operationally transmitted torque. On the other hand an arbor system is needed with fully defined and rigid connection between the arbor and the power tool. The thread connection is thereby needed to remain substantially unaffected by tilting torque and/or operational load torque. The present invention addresses these needs.
Further more, there also exists a need for an arbor system that provides a reliable form fitting of mechanically highly dissimilar materials of arbor and hole saw body. The present invention addresses this need as well.
Also, there exists a need for a quick release arbor system that provides a simple, robust and easily replaceable snap feature to prevent unintentional loosening during hole saw operation. The present invention addresses also this need.